14-Alexandrite

Question

Non linear speed control

Forum|Forum|4 years ago
January 31, 2022
2 replies
6690 views

Hi community , Once again I call on you .

my problem:

I have a mechanism with a non-linear movement

in input, I have a linear displacement, and in output I have an angular displacement

this displacement follows a behavior curve

I want to drive the input with a motor, so here is my problem.

I want to find a max speed value of motor to reach a given angular position. But also that time is linear

that is to say, if I want to go from 0 degrees to 60 degrees (for example) what will be my lowest linear displacement time (constant speed value at output), and what will be my motor control curve

the solution I found is cut the curve with linear parts,but I don't really like it because it's DIY

I don't see the way to get there, maybe with the derivative

If someone has an idea

1_linear-and-angular-speed.zip

Mechanical_Engineering

W

Werner_E

25-Diamond I

I don't see your attempt in the file you sent.

As far as I understand you are looking for a function

alpha -> speed in rev/s

Can you show the calculations necessary and the result for one or two example angles?

X

XDN

Author

14-Alexandrite

I'm having trouble explaining myself because I don't speak the language well.

example

if i want to move Alpha =60deg ( row 61 in alpha matrix)

the imput stroke is 32.355mm (row 61 in s matrix)

For 1 motor rev the imput stroke is :0.069mm

Capture d’écran 2022-01-31 130442.jpg Finally, i need to make 32.355mm

and so my motor must do 32.355/0.069 = 468.913 rev

max motor rev speed :0.287 rev/s but is non linear

if i cut the curve, and if that I admit a linear part from 0deg to 10deg

for 10 deg , imput is 2.682mm

2.682/0.069=38.87rev

time is :135.436s for travel 0 to 10deg

and now i assume my curve is linear from 10deg to 60deg

imput stroke 60deg =32.355mm

imput stroke 10deg = 2.682mm

32.355-2.682 = 29.673mm

29.673/0.069= 430.043rev

430.043/0.287=1498s

I don't know if I'm clear, but I want to come to this:

find max speed motor for each target value (row of alpha matrix) for a linear travel time

i want to move 0deg to 60deg with lineartravel, for this I can see that my motor must turn slowly at the beginning, then as quickly as possible at the end

the max speed end is 0.287rev/s so it is this value which is measured to evaluate the speeds at small angles

sorry for these confusing explanations, I think there may be a way with the derivative, but I can't find anything

W

Werner_E

25-Diamond I

0.02 this must be a mistake on my part

I guess the error was here

as you used the displacement per motor revolution and not per screw rev.

So it seems that the task is clear to me, unfortunately not the way how to solve it. I just became doubts about the method I sketched above as I would have two independent parameters to chose - the initial value for the velocity AND the constant velocity of alpha. It looks to me thats one too much. Maybe I'll see clearer tomorrow or one of my fellows here in he forum has a good idea 😉

BTW, what about my criticism that in your drawing small values of s would yield larger angles while in your sheet its the other way round. I guess that s should rather be the distance of the nut from a certain point near the motor/gear.
I made a model according to that but could not find dimensions which would yield results similar to those given in your sheet. So I suppose the real kinematics are somewhat more complicated and the drawing was just a simplification.